Baader 1¼" C2 Swan-Band Filter (15nm) – O III parallel - Contrast gain for comet hunters

Baader 1¼" C2 Swan-Band Filter (15nm) – O III parallel  - Contrast gain for comet hunters

The Baader C2 SWAN-Band-Filter with ≤ 15 nm Half-Band-Width isolates the two C2 lines at 511 and 514nm.

These two emission lines, named Swan bands after their discoverer, dominate the spectrum of a comet's gas tail in the visible range. The filter allows only the light from the two carbon bands to pass through and, among other things, blocks the ubiquitous stray light, similar to a nebula filter in deep-sky observation. Structures in the gas tail thus become clearer even under good observing conditions. At the same time, it completely blocks the OIII line at 501nm and below, which other Swan-Band filters allow to pass. This allows for even higher contrast, and comets with gas tails can be distinguished even better from those dominated by a dust tail (and where a SWAN filter provides only a small contrast enhancement). For ambitious comet observers, a SWAN filter is part of the basic equipment.

Just in time for the introduction of the new C2 Swan-Band filter, a bright comet, comet C/2022 E3 (ZTF), offered itself as a test object. Our customer Andreas Bringmann was one of our first testers.

This image was taken from the big city and with an almost full moon. You can clearly see the amount of "doubly ionized carbon" (the carbon excited to glow radiates only in the wavelengths 511 nm and 514 nm ) emitted by the comet. The filter shows the complete extension of the ion cloud around a comet.

The Baader SWAN-Filter has got all the advantages of the CMOS-optimized Baader filters:

• Increased contrast, matched for typical CMOS quantum efficiency and s/n ratio
• Reflex-Blocker coatings, for largest ever freedom from halos, even under most adverse conditions concerning aux-optics
• Identical filter thickness to existing standards, with utmost care for parfocality
• Blackened edges all around, with filter-lead-side-indicator in the form of a telescope-sided black outer rim, to additionally eliminate any reflection due to light falling onto the edge of a filter, making additional front-masks obsolete
• Each filter coated individually, with sealed coating edge (NOT cut out of a larger plate with coatings left exposed, read more)
• Life-Coat: evermore hard coatings to enable a non-aging coating for life – even in a most adverse environment